The spotted seal known as the larga seal or largha seal, is a member of the family Phocidae, is considered a "true seal". It inhabits ice waters of the north Pacific Ocean and adjacent seas, it is found along the continental shelf of the Beaufort, Chukchi and Okhotsk Seas and south to the northern Yellow Sea and it migrates south as far as northern Huanghai and the western Sea of Japan. It is found in Alaska from the southeastern Bristol Bay to Demarcation Point during the ice-free seasons of summer and autumn when spotted seals mate and have pups. Smaller numbers are found in the Beaufort Sea, it is sometimes mistaken for the harbor seal to which it is related and spotted seals and harbor seals mingle together in areas where their habitats overlap. The reduction in arctic ice floes due to global warming led to concerns that the spotted seal was threatened with extinction. Studies were conducted on its population numbers, with the conclusion, as of October 15, 2009, that the spotted seal population in Alaskan waters is not to be listed as endangered by NOAA.
The scientific name originated in the Greek word for seal and larga, the term used by the Siberian Tungus people for this seal. The English common name is comes from this seal's characteristic dark, irregularly shaped spots. Alaskan Eskimo names include issuriq, gazigyaq in St. Lawrence Island Yupik, qasigiaq in Inupiaq; the spotted seal is of the family, Phocidae, or "true seals". Compared to other true seals, they are intermediate in size, with mature adults of both sexes weighing between 180 and 240 pounds and measuring 4.59 to 6.89 ft the same size as a harbor seal or ribbon seal. The head of a spotted seal is round, with a narrow snout resembling that of a dog; the spotted seal has a small body and short flippers extending behind the body that provide thrust, while the small flippers in front act as rudders. The dense fur varies in color from silver to gray and white and is characterized by dark, irregular spots against the lighter background and covering the entire body. Males and females differ little in shape.
In places where their habitat overlaps with that of the harbor seal, they can be confused with them, as in Bristol Bay, Alaska. Like harbor seals, spotted seals have 34 teeth. Spotted seals are inhabitants of arctic or sub-arctic waters in the outer areas of ice floes during the breeding season, they tend not to live within dense drift ice. In the summer months they live on nearby shores. Spotted seals are separated into three populations; the Bering Sea population includes 100,000 in the western Bering Sea near Kamchatka, in the Gulf of Anadyr in Russia, in the eastern Bering Sea in Alaskan waters. A second population of about 100,000 seals breeds in the Sea of Okhotsk. A third population of about 3,300 seals is to the south in Liaodong Bay and Peter the Great Bay, Russia. There is a smaller population of 300 grey spotted seals living in waters off Baekryeong Island located far north of the west coast of South Korea. Spotted seals are shy and are difficult for humans to approach, they can be solitary in general but are gregarious and form large groups during pupping and molting seasons when they haul out on ice floes or, lacking ice, on land.
The numerically largest groups in Alaska are at Kasegaluk Lagoon in the Chukchi Sea, near Cape Espenburg in Kotzebue Sound, in Kuskokwim Bay on sandbars and shoals, where several thousand may collect. Sexual maturity is attained around the age of four. January to mid-April is the breeding season. Pup births peak in mid-March. Spotted seals are believed annually monogamous, during breeding season, they form "families" made up of a male and their pup, born after a 10-month gestation period. Average birth size is 26 lbs. Pups are weaned six weeks later; the maximum lifespan of the spotted seal is 35 years with few living beyond 25. Spotted seals dive to depths up to 1,000 ft. Juveniles eat krill and small crustaceans while adults eat a variety of fish including herring, arctic cod and capelin, they do not seem to vocalize a lot. They appear to vocalize more while in molting groups; when approached in these groups, they make various sounds such as growls, barks and roars. Based on satellite tracking conducted on Yellow Sea population, it was revealed that seals migrate more than 3,300 km.
On March 28, 2008, the U. S. National Oceanic and Atmospheric Administration initiated a status review under the Endangered Species Act to determine if listing this ice seal species under the ESA was warranted. After an 18-month review of the status of the spotted seal, NOAA announced on October 15, 2009 that two of the three spotted seal populations, together numbering 200,000 seals in or adjacent to Alaska, are not in danger of becoming extinct, nor are they to become so in the "foreseeable future" though global warming has caused a loss in arctic ice mass; the announcement stated: "We do not predict the expected fluctuations in sea ice will affect them enough to warrant listing at this time." In South Korea, spotted seals have been designated Natural Monument No. 331 and second-class endangered species. This is because the seals from South Korea travel to Dalian, China to breed every year where several thousands are harvested for their genitals and sealskin to be sold on the black market for Chinese medicine.
An environmental activist group Green Korea United is working with local Chi
King crabs are a taxon of crab-like decapod crustaceans chiefly found in cold seas. Because of their large size and the taste of their meat, many species are caught and sold as food, the most common being the red king crab. King crabs are thought to be derived from hermit crab-like ancestors, which may explain the asymmetry still found in the adult forms; this ancestry is supported by several anatomical peculiarities which are present only in king crabs and hermit crabs. Although some doubt still exists about this theory, king crabs are the most quoted example of carcinisation among the Decapoda; the evidence for this explanation comes from the asymmetry of the king crab's abdomen, thought to reflect the asymmetry of hermit crabs, which must fit into a spiral shell. Although classified among the hermit crabs in the superfamily Paguroidea, king crabs are now placed in a separate superfamily, Lithodoidea; this is not without controversy as there is a widespread consensus in the scientific community that king crabs are derived from hermit crabs and related to pagurid hermit crabs, therefore a separate superfamily in the classification poorly reflects the phylogenetic relationship of this taxon.
Species of the king crab, including Neolithodes diomedeae, use a species of sea cucumbers referred to as sea pigs as hosts and can be found on top of and under Scotoplanes. The Scotoplanes reduce the risk of predation for the N. diomedeae, while the Scotoplanes are not harmed from being hosts, which supports the consensus that the two organisms have a commensal relationship. Around 121 species are known, in 10 genera: Glyptolithodes is found chiefly in the Southern Hemisphere, but extending as far north as California, although all its closest relatives live in the Northern Hemisphere, its single species, G. cristatipes was placed in the genus Rhinolithodes. Red and blue king crabs are some of the most important fisheries in Alaska, however populations have fluctuated in the past 25 years and some areas are closed due to overfishing; the two species are similar in size and life history. Habitat is the main factor separating the range of red king crabs in the Bering Sea. Red king crabs prefer shallow, muddy or sandy habitats in Bristol Bay and Norton Sound, while blue king crabs prefer the deeper areas made up of cobble and rock that occur around the Pribilof, St. Matthew, St. Lawrence, the Diomede Islands.
Red king crabs have an 11-month brood cycle in their first reproductive year and a 12-month cycle thereafter. Both red and blue king crabs have planktotrophic larvae that undergo 4 zoeal stages in the water column and a non-feeding intermediate glaucothoe stage which seeks appropriate habitat on the sea floor; the red king crab, Paralithodes camtschaticus, is a large species, sometimes reaching a carapace width of 11 in and a leg span of 6 ft. Its natural range is the Bering Sea around the Kamchatka Peninsula area, between the Aleutian Islands and St. Lawrence Island, it can now be found in the Barents Sea and the European Arctic, where it was intentionally introduced and is now becoming a pest. The blue king crab, Paralithodes platypus, lives near St. Matthew Island, the Pribilof Islands, the Diomede Islands and there are populations along the coasts of Japan and Russia. Blue king crabs from the Pribilof Islands are the largest of all the king crabs, sometimes exceeding 18 lb in weight. Alaskan king crab fishing Deadliest Catch Media related to Lithodidae at Wikimedia Commons Data related to Lithodidae at Wikispecies
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage finds these names being applied to ophiuroids, which are referred to as brittle stars or basket stars. About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters, they are found from the intertidal zone down to 6,000 m below the surface. Starfish are marine invertebrates, they have a central disc and five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface, they are opportunistic feeders and are predators on benthic invertebrates. Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding.
They can reproduce both sexually and asexually. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence; the Asteroidea occupy several significant ecological roles. Starfish, such as the ochre sea star and the reef sea star, have become known as examples of the keystone species concept in ecology; the tropical crown-of-thorns starfish is a voracious predator of coral throughout the Indo-Pacific region, the northern Pacific sea star is considered to be one of the world's 100 worst invasive species. The fossil record for starfish is ancient, dating back to the Ordovician around 450 million years ago, but it is rather sparse, as starfish tend to disintegrate after death. Only the ossicles and spines of the animal are to be preserved, making remains hard to locate. With their appealing symmetrical shape, starfish have played a part in literature, legend and popular culture, they are sometimes collected as curios, used in design or as logos, in some cultures, despite possible toxicity, they are eaten.
Most starfish have five arms that radiate from a central disc. Some species have six or seven arms and others have 10–15 arms; the Antarctic Labidiaster annulatus can have over fifty. Having descended from bilateral organisms, starfish move in a bilateral fashion, with certain arms acting like the front of the animal; the body wall consists of a thin cuticle, an epidermis consisting of a single layer of cells, a thick dermis formed of connective tissue and a thin coelomic myoepithelial layer, which provides the longitudinal and circular musculature. The dermis contains an endoskeleton of calcium carbonate components known as ossicles; these are honeycombed structures composed of calcite microcrystals arranged in a lattice. They vary in form, with some bearing external granules and spines, but most are tabular plates that fit neatly together in a tessellated manner and form the main covering of the aboral surface; some are specialised structures such as the madreporite and paxillae. Pedicellariae are compound ossicles with forceps-like jaws.
They remove debris from the body surface and wave around on flexible stalks in response to physical or chemical stimuli while continually making biting movements. They form clusters surrounding spines. Paxillae are umbrella-like structures found on starfish; the edges of adjacent paxillae meet to form a false cuticle with a water cavity beneath in which the madreporite and delicate gill structures are protected. All the ossicles, including those projecting externally, are covered by the epidermal layer. Several groups of starfish, including Valvatida and Forcipulatida, possess pedicellariae. In Forcipulatida, such as Asterias and Pisaster, they occur in pompom-like tufts at the base of each spine, whereas in the Goniasteridae, such as Hippasteria phrygiana, the pedicellariae are scattered over the body surface; some are thought to assist in defence, while others aid in feeding or in the removal of organisms attempting to settle on the starfish's surface. Some species like Labidiaster annulatus, Rathbunaster californicus and Novodinia antillensis use their large pedicellariae to capture small fish and crustaceans.
There may be papulae, thin-walled protrusions of the body cavity that reach through the body wall and extend into the surrounding water. These serve a respiratory function; the structures are supported by collagen fibres set at right angles to each other and arranged in a three-dimensional web with the ossicles and papulae in the interstices. This arrangement enables both easy flexion of the arms by the starfish and the rapid onset of stiffness and rigidity required for actions performed under stress; the water vascular system of the starfish is a hydraulic system made up of a network of fluid-filled canals and is concerned with locomotion, food manipulation and gas exchange. Water enters the system through the madreporite, a porous conspicuous, sieve-like ossicle on the aboral surface, it is linked through a stone canal lined with calcareous material, to a ring canal around the mouth opening. A set of radial canals leads off this. There are short lateral canals branching off alternately to either side of the radial canal, each ending in an ampulla.
These bulb-shaped organs are joined to tube feet on the exterior of the animal by short linking canals that pass through ossicles in the ambulacral groove. There are two rows of tube feet but in some species, the lateral c
Halibut is a common name principally applied to the two flatfish in the genus Hippoglossus from the family of right-eye flounders. Less and in some regions only, other species of flatfish are referred to as being halibuts; the word is derived for its popularity on Catholic holy days. Halibut are demersal fish and are regarded as a food fish. Species of the genus Hippoglossus Atlantic halibut, Hippoglossus hippoglossus – lives in the North Atlantic Pacific halibut, Hippoglossus stenolepis – lives in the North Pacific Ocean The Pacific halibut is the world's largest flatfish; the IGFA record was broken off the waters of Norway in July 2013 by a 515-pound 8.6 foot fish. This was awaiting certification as of 2013. In July 2014, a 482-pound Pacific halibut was caught in Alaska. Halibut are dark brown on the top side with an off-white underbelly and have small scales invisible to the naked eye embedded in their skin. Halibut are symmetrical at birth with one eye on each side of the head. About six months during larval metamorphosis one eye migrates to the other side of the head.
The eyes are permanently set once the skull is ossified. At the same time, the stationary-eyed side darkens to match the top side, while the other side remains white; this color scheme disguises is known as countershading. Halibut feed on any fish or animal they can fit into their mouths. Juvenile halibut feed on other bottom-dwelling organisms. Animals found in their stomachs include sand lance, crab, hermit crabs, sculpin, pollock and flounder, as well as other halibut. Halibut live at depths ranging from a few meters to hundreds, although they spend most of their time near the bottom, halibut may move up in the water column to feed. In most ecosystems, the halibut is near the top of the marine food chain. In the North Pacific, common predators are killer whales, salmon sharks and humans; the North Pacific commercial halibut fishery dates to the late 19th century and today is one of the region's largest and most lucrative. In Canadian and US waters, long-line fishing predominates, using chunks of octopus or other bait on circle hooks attached at regular intervals to a weighted line that can extend for several miles across the bottom.
The fishing vessel retrieves the line after several hours to a day. The effects of long-line gear on habitats are poorly understood, but could include disturbance of sediments, benthic structures, other structures. International management is thought to be necessary, because the species occupies waters of the United States, Canada and Japan, matures slowly. Halibut do not reproduce until age eight, when about 30 in long, so commercial capture below this length prevents breeding and is against US and Canadian regulations supporting sustainability. Pacific halibut fishing is managed by the International Pacific Halibut Commission. For most of the modern era, halibut fishery operated as a derby. Regulators declared time slots when fishing was open and fisherman raced to catch as many pounds as they could within that interval; this approach accommodated unlimited participation in the fishery while allowing regulators to control the quantity of fish caught annually by controlling the number and timing of openings.
The approach led to unsafe fishing, as openings were set before the weather was known, forcing fisherman to leave port regardless of the weather. The approach limited fresh halibut to the markets to several weeks per year, when the gluts would push down the price received by fishermen. In 1995, US regulators allocated individual fishing quotas to existing fishery participants based on each vessel's documented historical catch. IFQs grant to holders a specific proportion of each year's total allowable catch; the fishing season is nine months. The IFQ system improved both safety and product quality by providing a stable flow of fresh halibut to the marketplace. Critics of the program suggest, since holders can sell their quota and the fish are a public resource, the IFQ system gave a public resource to the private sector; the fisheries were managed through a treaty between the United States and Canada per recommendations of the International Pacific Halibut Commission, formed in 1923. A significant sport fishery in Alaska and British Columbia has emerged, where halibut are prized game and food fish.
Sport fisherman use large rods and reels with 80–150 lb line, bait with herring, large jigs, or whole salmon heads. Halibut fight strenuously when exposed to air. Smaller fish will be pulled on board with a gaff and may be clubbed or punched in the head to prevent them from thrashing around on the deck. In both commercial and sport fisheries, standard procedure is to shoot or otherwise subdue large halibut over 150–200 lb before landing them. Alaska's sport fishery is an element of the state's tourism economy. Halibut are boiled, deep-fried or grilled while fresh. Smoking is more difficult with halibut meat than it is with salmon, due to its ultra-low fat content. Eaten fresh, the meat requires little seasoning. Halibut is noted for its dense and firm texture. Halibut have been an important food source to Alaska Natives and Canadian First Nations, continue to be a key element to many coastal subsistence economies. A
Salmon is the common name for several species of ray-finned fish in the family Salmonidae. Other fish in the same family include trout, char and whitefish. Salmon are native to tributaries of the North Pacific Ocean. Many species of salmon have been introduced into non-native environments such as the Great Lakes of North America and Patagonia in South America. Salmon are intensively farmed in many parts of the world. Salmon are anadromous: they hatch in fresh water, migrate to the ocean return to fresh water to reproduce. However, populations of several species are restricted to fresh water through their lives. Folklore has it. Tracking studies have shown this to be true. A portion of a returning salmon run may spawn in different freshwater systems. Homing behavior has been shown to depend on olfactory memory. Salmon date back to the Neogene; the term "salmon" comes from the Latin salmo, which in turn might have originated from salire, meaning "to leap". The nine commercially important species of salmon occur in two genera.
The genus Salmo contains the Atlantic salmon, found in the north Atlantic, as well as many species named trout. The genus Oncorhynchus contains eight species which occur only in the North Pacific; as a group, these are known as Pacific salmon. Chinook salmon have been introduced in New Patagonia. Coho, freshwater sockeye, Atlantic salmon have been established in Patagonia, as well. † Both the Salmo and Oncorhynchus genera contain a number of species referred to as trout. Within Salmo, additional minor taxa have been called salmon in English, i.e. the Adriatic salmon and Black Sea salmon. The steelhead anadromous form of the rainbow trout migrates to sea, but it is not termed "salmon". A number of other species have common names which refer to them as being salmon. Of those listed below, the Danube salmon or huchen is a large freshwater salmonid related to the salmon above, but others are marine fishes of the unrelated Perciformes order: Eosalmo driftwoodensis, the oldest known salmon in the fossil record, helps scientists figure how the different species of salmon diverged from a common ancestor.
The British Columbia salmon fossil provides evidence that the divergence between Pacific and Atlantic salmon had not yet occurred 40 million years ago. Both the fossil record and analysis of mitochondrial DNA suggest the divergence occurred by 10 to 20 million years ago; this independent evidence from DNA analysis and the fossil record rejects the glacial theory of salmon divergence. Atlantic salmon reproduce in northern rivers on both coasts of the Atlantic Ocean. Landlocked salmon live in a number of lakes in eastern North America and in Northern Europe, for instance in lakes Sebago, Ladoga, Saimaa, Vänern, Winnipesaukee, they are not a different species from the Atlantic salmon, but have independently evolved a non-migratory life cycle, which they maintain when they could access the ocean. Chinook salmon are known in the United States as king salmon or blackmouth salmon, as spring salmon in British Columbia. Chinook are the largest of all Pacific salmon exceeding 14 kg; the name tyee is used in British Columbia to refer to Chinook over 30 pounds, in the Columbia River watershed large Chinook were once referred to as June hogs.
Chinook salmon are known to range as far north as the Mackenzie River and Kugluktuk in the central Canadian arctic, as far south as the Central California coast. Chum salmon are known as dog, keta, or calico salmon in some parts of the US; this species has the widest geographic range of the Pacific species: south to the Sacramento River in California in the eastern Pacific and the island of Kyūshū in the Sea of Japan in the western Pacific. Coho salmon are known in the US as silver salmon; this species is found throughout the coastal waters of Alaska and British Columbia and as far south as Central California. It is now known to occur, albeit infrequently, in the Mackenzie River. Masu salmon or cherry salmon are found only in the western Pacific Ocean in Japan and Russia. A land-locked subspecies known as the Taiwanese salmon or Formosan salmon is found in central Taiwan's Chi Chia Wan Stream. Pink salmon, known as humpies in southeast and southwest Alaska, are found from northern California and Korea, throughout the northern Pacific, from the Mackenzie River in Canada to the Lena River in Siberia in shorter coastal streams.
It is the smallest of the Pacific species, with an average weight of 1.6 to 1.8 kg. Sockeye salmon are known in the US as red salmon; this lake-rearing species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaidō island in Japan in the western Pacific and as far north as Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. Although most adult Pacific salmon feed on small fish and squid, sockeye feed on plankton they filter through gill rakers. Kokanee salmon are the land-locked form of sockeye salmon. Danube salmon, or huchen, are the largest permanent freshwater salmonid species. Salmon eggs are laid in freshwater streams at high latitudes; the eggs hatch into alevin or sac fry
Lowell Creek Diversion Tunnel
The Lowell Creek Diversion Tunnel is a flood control project located in Seward, United States. The project was constructed to alleviate flooding of Lowell Creek in Seward, it was the first flood control project completed by the United States Army Corps of Engineers in Alaska. Lowell Creek ran through Seward along what is now Jefferson Street. Beginning with the town's establishment in 1903, the fast-moving stream produced one to three severe floods a year until the tunnel was built in 1939; the floods carried large amounts of debris from the mountains. In 1927 the Alaska Railroad constructed a small diversion dam and flume to carry debris down Jefferson Street to drain into Resurrection Bay. However, by 1937 these structures had deteriorated beyond repair; the Army Corps of Engineers began construction of the new project in August 1939. The project consisted of: a diversion dam, 400 feet in length and up to 25 feet high that diverted the creek away from its original path. Completed in 1940, this system withstood the 1964 Alaska earthquake, as well as severe floods in 1966, 1986, 1995, which brought the water level within inches of cresting the dam.
The tunnel was listed on the National Register of Historic Places in 1977. Though the project has prevented significant flooding of the city of Seward, debris continues to accumulate at the outlet of the flume and the city must work to move the debris further into the bay. With the significant risk of debris accumulation during a flooding event, new projects are being considered to replace the diversion tunnel — including construction of a new, wider tunnel through Bear Mountain at a cost of $30 million, or an aqueduct underneath Jefferson Street. National Register of Historic Places listings in Kenai Peninsula Borough, Alaska
Sea urchins or urchins are spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres, their tests are round and spiny from 3 to 10 cm across. Sea urchins move crawling with their tube feet, sometimes pushing themselves with their spines, they feed on algae but eat slow-moving or sessile animals. Their predators include sea otters, wolf eels, triggerfish. Like other echinoderms, urchins have fivefold symmetry as adults, but their pluteus larvae have bilateral symmetry, indicating that they belong to the Bilateria, the large group of animal phyla that includes chordates, arthropods and molluscs, they are distributed across all the oceans, all climates from tropical to polar, inhabit marine benthic habitats from rocky shores to hadal zone depths. Echinoids have a rich fossil record dating back to the Ordovician, some 450 million years ago, their closest relatives among the echinoderms are the sea cucumbers.
The animals have been studied since the 19th century as model organisms in developmental biology, as their embryos were easy to observe. Species such as the slate pencil urchin are popular in aquariums, where they are useful for controlling algae. Fossil urchins have been used as protective amulets. Sea urchins are members of the phylum Echinodermata, which includes sea stars, sea cucumbers, brittle stars, crinoids. Like other echinoderms, they have five-fold symmetry and move by means of hundreds of tiny, adhesive "tube feet"; the symmetry is not obvious in the living animal, but is visible in the dried test. The term "sea urchin" refers to the "regular echinoids", which are symmetrical and globular, includes several different taxonomic groups, with two subclasses: Euechinoidea and Cidaroidea or "slate-pencil urchins", which have thick, blunt spines, with algae and sponges growing on them; the "irregular" sea urchins are an infra-class inside the Euechinoidea, called Irregularia, include Atelostomata and Neognathostomata.
Irregular echinoids include: flattened sand dollars, sea biscuits, heart urchins. Together with sea cucumbers, they make up the subphylum Echinozoa, characterized by a globoid shape without arms or projecting rays. Sea cucumbers and the irregular echinoids have secondarily evolved diverse shapes. Although many sea cucumbers have branched tentacles surrounding their oral openings, these have originated from modified tube feet and are not homologous to the arms of the crinoids, sea stars, brittle stars. Urchins range in size from 3 to 10 cm, although the largest species can reach up to 36 cm, they have a rigid spherical body bearing moveable spines, which gives the class the name Echinoidea. The name "urchin" is an old word for hedgehog; the name is derived from Latin ericius, hedgehog. Like other echinoderms, sea urchin early larvae have bilateral symmetry, but they develop five-fold symmetry as they mature; this is most apparent in the "regular" sea urchins, which have spherical bodies with five sized parts radiating out from their central axes.
The mouth is at the anus at the top. Several sea urchins, including the sand dollars, are oval in shape, with distinct front and rear ends, giving them a degree of bilateral symmetry. In these urchins, the upper surface of the body is domed, but the underside is flat, while the sides are devoid of tube feet; this "irregular" body form has evolved to allow the animals to burrow through sand or other soft materials. Sea urchins may appear to be incapable of moving. Sometimes the most visible sign of life is the spines, which are attached to ball-and-socket joints and can point in any direction. Sea urchins have no visible eyes, legs, or means of propulsion, but can move but over hard surfaces using adhesive tube feet, working in conjunction with the spines; the internal organs are enclosed in a hard shell or test composed of fused plates of calcium carbonate covered by a thin dermis and epidermis. The test is rigid, divides into five ambulacral grooves separated by five interambulacral areas; each of these areas consists of two rows of plates, so the sea urchin test includes 20 rows of plates in total.
The plates are covered in rounded tubercles which contain the sockets to which the spines are attached by ball and socket joints. The inner surface of the test is lined by peritoneum. Sea urchins convert aqueous carbon dioxide using a catalytic process involving nickel into the calcium carbonate portion of the test. Most species have two series of spines and secondary, distributed over the surface of the body, with the shortest at the poles and the longest at the equator; the spines are hollow and cylindrical. Contraction of the muscular sheath that covers the test causes the spines to lean in one direction or another, while an inner sheath of collagen fibres can reversibly change from soft to rigid which can lock the spine i